The cor anglais is a transposing instrument pitched in F, a perfect fifth lower than the oboe (a C instrument), and is consequently approximately one and a half times the length of the oboe. The fingering and playing technique used for the cor anglais are essentially the same as those of the oboe, and most oboists double on the cor anglais. Music for the cor anglais is thus written a perfect fifth higher than the instrument actually sounds. Because the cor anglais normally lacks the lowest B♭ key found on most oboes, its sounding range stretches from E3 (written B natural) below middle C to C6 two octaves above middle C.

Its pear-shaped bell gives it a more covered timbre than the oboe, closer in tonal quality to the oboe d'amore. Whereas the oboe is the soprano instrument of the oboe family, the cor anglais is generally regarded as the tenor member of the family, and the oboe d'amore—pitched between the two in the key of A—as the alto member.[1] The cor anglais is perceived to have a more mellow and plaintive tone than the oboe. Its appearance differs from the oboe in that the reed is attached to a slightly bent metal tube called the bocal, or crook, and the bell has a bulbous shape. It is also much longer.

The cor anglais is usually notated in the treble clef, a perfect fifth higher than sounding. Some composers notated it in the bass clef, when the lower register was persistently used,[2] and historically several other options were employed. Alto clef written at sounding pitch is occasionally used, even by as late a composer as Sergei Prokofiev. In late-18th and early-19th-century Italy, where the instrument was often played by bassoonists instead of oboists, it was notated in the bass clef an octave below sounding pitch (as found in Rossini'sOverture to William Tell). French operatic composers up to Fromental Halévy notated the instrument at sounding pitch in the mezzo-soprano clef, which enabled the player to read the part as if it were in the treble clef.[1]

Although the instrument usually descends only to (written) low B♮, continental instruments with an extension to low B♭ (sounding E♭) have existed since early in the 19th century.[3] Examples of works requiring this note (while acknowledging its exceptional nature) include Arnold Schoenberg’s Gurre-Lieder and Gustav Mahler's Das Lied von der Erde. Antonín Dvořák, in his Scherzo Capriccioso, even writes for the cor anglais down to low A, though it seems unlikely that such an extension ever existed.[4]

Reeds used to play the cor anglais are similar to those used for an oboe, consisting of a piece of cane folded in two. While the cane on an oboe reed is mounted on a small metal tube (the staple) partially covered in cork, there is no such cork on a cor anglais reed, which fits directly on the bocal. The cane part of the reed is wider and longer than that of the oboe. Unlike American style oboe reeds, cor anglais reeds typically have wire at the base, approximately 5 millimeters from the top of the string used to attach the cane to the staple. This wire serves to hold the two blades of cane together and stabilize tone and pitch.

Perhaps the best-known makers of modern cors anglais are the French firms of F. Lorée, Marigaux and Rigoutat, the British firm of T. W. Howarth, and the American firm Fox. Instruments from smaller makers, such as A. Laubin, are also sought after. Instruments are usually made from African Blackwood (aka Grenadilla), although some makers offer instruments in a choice of alternative woods as well, such as cocobolo (Howarth) or violet wood (Lorée), which are said to alter the voice of the cor anglais slightly, reputedly making it even more mellow and warmer. Fox has recently made some instruments in plastic resin.

The term cor anglais is French for English horn, but the instrument is neither from England nor related to the (French) horn. The instrument originated in Silesia about 1720, when a bulb bell was fitted to a curved oboe da caccia-type body by the Weigel family of Breslau. The two-keyed, open-belled, straight tenor oboe (French taille de hautbois, "tenor oboe"), and more particularly the flare-belled oboe da caccia, resembled the horns played by angels in religious images of the Middle Ages. This gave rise in German-speaking central Europe to the Middle High German name engellisches Horn, meaning angelic horn. Because engellisch also meant English in the vernacular of the time, the "angelic horn" became the "English horn." In the absence of any better alternative, the curved, bulb-belled tenor oboe then retained the name even after the oboe da caccia fell into disuse around 1760.[5] The name first appeared on a regular basis in Italian, German, and Austrian scores from 1741 on, usually in the Italian form corno inglese.[6]

The earliest known orchestral part specifically for the instrument is in the Vienna version of Niccolò Jommelli's opera Ezio dating from 1749,[7] where it was given the Italian name corno inglese.[8]Gluck and Haydn followed suit in the 1750s,[9] and the first English horn concertos were written in the 1770s. Considering the name "cor anglais," it is ironic that the instrument was not used in France until about 1800 or in England until the 1830s.[9] The OED lists the first mention of the instrument in the English language in a 1775 musical travelogue ("...I plainly distinguished..the English horn") and in the Penny Cyclopedia in 1838 ("The English Horn, or Corno Inglese, is a deeper-toned oboe..."), while the first identified printed use of the term cor anglais in English was in 1870.[10]In the UK the instrument is colloquially generally referred to as the "cor".[1] The local equivalent for "English horn" is used in most other European languages, while a few languages use their equivalent of "alto oboe".

As the cor anglais has a bent metal pipe (the bocal) that connects the reed to the instrument proper, the suggestion has been made that anglais might be a corruption of Middle Frenchanglé (angular, or bent at an angle, angulaire in modern French),[11] but this has been rejected on grounds that there is no evidence of the term cor anglé before it was offered as a possible origin of anglais in the 19th century.[12]

Igor Stravinsky's Pastorale for soprano and piano (1907), in the composer's own arrangements for soprano, oboe, English horn, clarinet, and bassoon (1923), and violin, oboe, English horn, clarinet, and bassoon (1933)

^Adam Carse, Musical Wind Instruments: A History of the Wind Instruments Used in European Orchestras and Wind-Bands from the Later Middle Ages Up to the Present Time (London: Macmillan and Co., 1939): 144.

^Adam Carse, Musical Wind Instruments: A History of the Wind Instruments Used in European Orchestras and Wind-Bands from the Later Middle Ages Up to the Present Time (London: Macmillan and Co., 1939): 143; Sybil Marcuse, "Cor anglais", in Musical Instruments: A Comprehensive Dictionary, revised edition, The Norton Library (New York: W. W. Norton, 1975). ISBN 0-393-00758-8.